Method and means for extending life of ion sensing electrode

ABSTRACT

Method and means for extending the useful life of an electrode utilized for measuring the ion concentration or activity of solutions. The electrode embodies an ion sensitive barrier containing a macrocyclic compound, mineral oil, preferably an aromatic component, and a sufficient amount of a compound lipid to render the barrier substantially solid. The life of the electrode is extended by subjecting the ion sensitive barrier, during storage or non-use of the electrode, to the vapors of an aromatic component, preferably a phenylether.

111 3,715,297 1 1 Feb. 6, 1973 Primary Examiner-T. Tung Attorney-ThomasL. Peterson and Robert J. Steinmeyer [57] ABSTRACT Method and means forextending the useful life of an electrode utilized for measuring the ionconcentration or activity of solutions. The electrode embodies an ionsensitive barrier containing a macrocyclic compound, mineral oil,preferably an aromatic component, and a sufficient amount of a compoundlipid to render the barrier substantially solid. The life of theelectrode is extended by subjecting the ion sensitive barrier, duringstorage or non-use of the electrode, to the vapors of an aromaticcomponent, preferably a phenylether.

32 Claims, 1 Drawing Figure .204/195 M .G() In 27/46 United StatesPatent Cosgrove et a1.

[54] METHOD AND MEANS FOR EXTENDING LIFE OF ION SENSING ELECTRODE [75]Inventors: Richard E. Cosgrove, Los Angeles;

Irwin H. Krull; Charles A. Mask, both of Garden Grove, all of Calif.

[73] Assignee: Beckman Instruments, Inc., Fullerton, Calif.

[22] Filed: July 20, 1970 [21] Appl. No.: 56,509

[51] Int.

[58] Field of Search....204/1 T, 195 A, 195 L, 195 M [56] ReferencesCited UNITED STATES PATENTS 2/1971 Simon.

PATENTEDFEB 6 I975 5i a i I \5 i i .5

INVENTORS RICHARD E.COSGROVE IRWIN H. KRULL CHARLES A. MASK eygj/myi225.

ATTORNEY METHOD AND MEANS FOR EXTENDING LIFE OF ION SENSING ELECTRODECROSS-REFERENCE TO RELATED APPLICATION The invention disclosed herein isrelated to and embodies some of the features of the inventiondisclosedin copending application of Richard Cosgrove et al. e'ntitledElectrochemical Electrode, Ser. No. 50,746 filed June 29, 1970.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates generally to an electrochemical electrode for measuring the ionconcentration or activity of a solution and, more particularly, to amethod and means for extending the useful life of such an electrode.

2. Description of the Prior Art In the foregoing Cosgrove et al.application, there are described various electrodes for measuring thepotassium and ammonium ion activities of solutions. The ion sensitivebarrier of each electrode contains a macrocyclic compound, mineral oil,preferably an aromatic constituent, and a sufficient amount of acompound lipid to render the barrier substantially solid. Suchelectrodes produce essentially a theoretical or Nernst response for aperiod of about two weeks, and thereafter the response of the electrodesdecreases, thus limiting the useful life of the electrodes. Therefore,what is needed is some means for extending the lives of these types ofelectrodes.

SUMMARY OF THE INVENTION The principal object of the present inventionis to provide a method and means for extending the life of an ionmeasuring electrode employing an essentially solid ion sensitive barriercontaining a macrocyclic compound.

According to the principal aspect of the present invention, the ionsensitive barrier of an electrode of the type described in the saidCosgrove et al. application is subjected to the vapors of an aromaticcomponent, such as a phenylether, when the electrode is in storage ornot in use. Preferably the aromatic component is located in a closedbottle having an opening in its cap receiving the sensing end of the ionmeasuring electrode. When it is desired to utilize the electrode tomeasure the ion concentration of a solution, the electrode is simplywithdrawn from the bottle and immersed in the test solution. By sotreating the ionsensitive barrier of the electrodes of the typedisclosed in the Cosgrove et al. application, the lives of theelectrodes are extended substantially.

Other objects, aspects and advantages of the invention will becomeapparentfrom the following description taken in connection with theaccompanying draw- BRIEF DESCRIPTION OF THE DRAWING The drawingillustrates, in partial longitudinal section, an ion measuring electrodemounted in a storage bottle containing an aromatic component inaccordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS concentrically mountedelectrical connectors 22 and 24 which protrude from the rear of the cap.These connectors are separated by a plastic sleeve, not shown. The innerconnector 24 is connected to a metal wire 26 that extends into a glasstube 28 which is retained within the body 16 by means of the cap 18. Theouter connector 22 is connected to a cylindrical metal electrostaticshield, not shown, which is embedded within the wall of the body 16.

The end of the glass tube 28 is closed by an ion sensitive barrier 30.The end of the wire 26 terminates in an internal half cell 32,preferably silver-silver chloride, which is immersed in a body ofelectrolyte 34 contained in the lower portion-of the tube 28.

Preferably a perforated membrane 36 is sealed across the lower end ofthe tube 28 to provide a protective covering for the ion sensitivebarrier 30. The membrane may be a collodion film, polyethylene,tetrafluoroethylene, or the like.

The barrier 30 is substantially solid and immiscible with aqueoussolutions. It contains a mixture of a macrocyclic compound, mineral oiland a compound lipid. Preferably the barrier also contains an aromaticcomponent, although it is not required.

Desirable macrocyclic compounds include the monactin series, whichincludes nonactin, monactin, dinactin, and trinactin, valinomycin, andanalogs having its ion selective character, and enniatin B. It has alsobeen found that at least some macrocyclic polyether compounds willproduce the results desired. In particular, a macrocyclic polyethersynthesized by C. J. Pedersen of the Elastomer Branch of E.I. duPontdeNemours and Company, Inc. has been successfully employed and it can beobserved that the selected polyether [hereafter referred to as -I]operates as an ion selective medium by exhibiting the capability offorming complexes with potassium ions. The particular composition hasbeen identified as containing eighteen ring atoms and six ring oxygens.Pedersen refers to this class of compounds as crown compounds and in hisnomenclature this composition is dicyclohexyl-l8 crown-6. Reference maybe made to the following literature reference for furtheridentification: Cyclic Polyethers and Their Complex with Metal Salts,"Journal of American Chemical Society, Volume 89, pp. 7017-7036 [l967]byC. .I. Pedersen.'Gramicidin, a cyclopeptide, and cyclohexyl-lS-crown-Scan also be used.

Suitable mineral oils are Nujol sold by Plough, Inc. and Vaseline, whichis a longer chain mineral oil, sold by Chesebrough-Ponds Inc. Examplesof suitable aromatic components are I nitrobenzene, phenylethers,

chlorobenzene, bromobenzene and alkylated aromatics. The aromaticcomponent may be either a solid or liquid.

The compound lipid is provided in a sufficient quantity to render thebarrier substantially solid, that is, in the form of a heavy putty.Compound lipids are esters of fatty acids with alcohols and containingother groups in addition to alcohols and acids. Examples of suitablecompound lipids are phosphatides or phospholipids [such as lecithin,lysolecithin, cephalin, inosital lipids and sphingomyelin], phosphatidicacids, glycolipids, and sulfolipidspThese compounds are solid at roomtemperature and have a waxy-like texture [as opposed to a regularcrystalline. material]. They are insoluble in water [but may swell inits presence]. They function as a surfactant and are capable ofemulsifying nonhomogeneous solutions. Commercial phosphatides orphospholipids, as they are also called, are often termed lecithinalthough lecithin is actually the designation of one of the purephosphatides. They are also sometimes called phosphatidycholine,lecithol, vitellin, kelecin and phospholutein granulestin. Because oftheir abundance and economy, such commercial phosphatides [which will bedesignated as lecithin hereinafter] are the preferred compound lipidsfor use in the barrier 30. Although only lecithin will be referred tohereinafter in this description, it will be understood that othercompound lipids mentioned above as well as any other materials havingthe aforementioned properties may be utilized in forming the barrier 30.

For an ion sensitive barrier which is selectively sensitive to potassiumions, valinomycin is the preferred macrocyclic compound and aphenylether is the preferred aromatic component, while Nujol is thepreferred mineral oil. The macrocyclic compound must be provided insufficient quantity to render the barrierselectively sensitive to theion being determined. By way of example, the ratio by weight of themineral oil, aromatic component, lecithin and valinomycin in a potassiumion sensitive electrode may be approximately l:1:6:0.04. In other words,the barrier contains about three times as much by weight of lecithinthan the other constituents. Satisfactory barriers have also been made,however, containing only about twice as much lecithin than the otherconstituents mentioned above. In addition, successful barriers have beenproduced wherein the aromatic component was entirely replaced by mineraloil so that the ratio of mineral oil, lecithin, and valinomycin wasabout 2:6:0.04. However, such barrier exhibited slightly less timestability than the barrier containing the aromatic component.

For an electrode which is selectively sensitive to ammonium ions in thepresence of other cations, the ion sensitive barrier 30 containsnonactin as the macrocyclic compound, together with the other threeconstituents mentioned above. Preferably, for an ammonium ion sensitivebarrier, the mineral oil is Nujol and the aromatic component is either2-phenyloxybiphenyl or bromodiphenylether. The preferred ratio by weightof t the Nujol, aromatic component, lecithin and nonactin is about 1:116:0.1.

If a collodion membrane 36 is employed, as the first step to constructthe electrode 10 the forward end of the glass tube 28 is immersed in asolution of collo'dion,

such as Collodion-Flexible sold by Merck. This material comprisescellulose nitrate dissolved in a mixture of ether, ethanol, castor oiland camphor. Upon withdrawing the tube from the solution, a thin firm 5membrane will cure and become sealed to the end of the tube, thusproviding the protective cover 36. Openings are provided in the membrane36 adjacent to the barrier material 30 to permit free ion passage fromthe sample solution to the barrier. Three openings each having adiameter of about 0.010 inch are adequate. Such openings may be made byforcing a wire ofthe aforementioned dimension through the membrane 36.The barrier 30 is provided in the tube 28 by first dissolving themixture of aromatic component, mineral oil, macrocyclic compound andlecithin in a suitable highly volatile solvent, such as chloroform, toform a solution. By the use of a syringe inserted through the rear end[not shown] of the tube 28, this solution is delivered to the forwardend of the tube. The solution in the tube is allowed to cure at roomtemperature, whereupon the chloroform will evaporate thus leaving thesolid barrier 30. Thereafter, the electrolyte 34 is delivered by asyringe to the interior of the tube 28 through the rear end of the tube.The tube 28 is then mounted in the hollow body 16 of the electrode withthe internal half cell 28 received through the rear end of the tube 28.The assembly is then fixedly retained within the body 16 by means of thecap 18.

It is to be understood that the aforementioned electrode is merely anexample of a suitable electrode assembly which may employ the ionsensitive barrier material 30. Obviously other forms of electrodes couldbe utilized. For example, the electrode could comprise simply a hollowbody closed by a cap having openings extending through the forward endthereof which are filled with the barrier material 30. In such anassembly, the interior of the electrode body would be filled with theelectrolyte in which the internal half cell is immersed.

As stated previously, electrodes of the aforemen tioned type produceessentially Nernst or theoretical response in both single and mixed ionsolutions for a period of about 2 weeks. Thereafter, the output of theelectrodes diminishes, thus limiting the useful lives of the electrodes.In accordance with the present invention, we have discovered that bysubjecting the ion sensitive barrier 30 of the electrode 10, when theelectrode is in storage or not in use, to the vapors of an aromaticcomponent, the useful life of the electrode is greatly extended.Preferably, the barrier 30 is so treated when the electrode is not inuse by mounting the sensing end 12 of the electrode within a closedcontainer 38 containing the aromatic component. The container comprisesan open bottle 40 closed by a threaded cap 42. The cap has a centralopening 44 slidably receiving the electrode 10 in sealing relationship.The container 38 is preferably formed of a plastic material such aspolyethylene, it being understood, of course, that the container may beformed of other materials which are not attacked by the aromaticcomponent. The aromatic component is preferably immobilized within thecontainer 38 remote from the sensing end 12 of the electrode. For thispurpose, a sponge 46 is glued to the bottom of the container 38 and thearomatic component is impregnated in the sponge. If the aromaticcomponent vapors of such aromatic component minimize the loss throughevaporation or otherwise of the more volatile components, including thearomatic constituent, in the barrier 30.

The advantages of the present invention will be appreciated from thefollowing examples:

EXAMPLE 1 A potassium ion measuring electrode as described herein andshown in the drawing employing an ion sensitive barrier comprising amixture of about equal parts by weight of Nujol mineral oil anddiphenylether, lecithin in a weight ratio to the combined weights of themineral oil and diphenylether of approximately 3:1, and 1 percent byweight of valinomycin. The lecithin which was used is sold under thetrade name W.'H.O. Brand Lecithin, by Western Health Organization,located in Los Angeles, Calif. This lecithin is derived from soy beans.The electrode was connected together with a standard calomel referenceelectrode to a conventional pH meter. The sensing electrode was testedin test solutions ranging from M to 10'' M potassium ion with abackground of 0.2 M sodium ion. The output of the electrode wasapproximately Nernst upon initial testing. After the electrode stood 'inroom atmosphere for approximately 4 days, its output decreasedapproximately 5 millivolts. After the electrode stood in room atmospherefor 3 additional days, its output dropped approximately anothermillivolts. Thus, the useful life of the electrode diminished rapidlyafter approximately 7 days of the electrode being exposed to roomatmosphere.

EXAMPLE 2 A potassium ion measuring electrode identical to thatdescribed in Example 1 was made except that the electrode contained 5percent by weight valinomycin. The electrode was tested periodicallythroughout a 105 day period in the same test solutions described inExample l. Between tests the electrode was exposed to an atmosphere ofdiphenylether in accordance with the present invention. Even after theend of such period, the electrode did not show any appreciable loss inoutput when tested in the mixed ion solutions of potassium and sodium.

EXAMPLE 3 Two potassium ion measuring electrodes were constructed asdescribed hereinbefore. The barrier of one of the electrodes contained 2mg. valinomycin, 0.05 g. Nujol, 0.05 g. phenyloxylbiphenyl and 0.3 g.lecithin while the barrier of the other electrode contained 2 mg.valinomycin, 0.05 g. Nujol, 0.05 g. bromodiphenylether and 0.3 g.lecithin. The electrodes were initially soaked for 2 hours and thentested in a variety of mixed potassium and sodium ion solutions. Theoutput of the electrodes was essentially Nernst. The electrodes werethen left standing in room atmosphere for a period of l5 days and againtested. The output of the electrodes after the 15 day exposure to roomatmosphere reduced to about one half of Nernst response.

EXAMPLE 4 Electrodes identical to those described in Example 3 abovewere initially tested, thereafter exposed to an atmosphere ofdiphenylether for a period of 15 days and then retested in the testsolutions. The output of the electrodes decreased only about 2 or 3millivolts, thus showing that for a period of at least 15 days theexposure of the-barriers of these electrodes to an aromatic componentsubstantially increased the useful lives of the electrodes.

EXAMPLE 5 Two potassium ion measuring electrodes as described hereinwere constructed each employing an ion sensitive barrier containing 2mg. valinomycin, 0.1 g. Nujol, and 0.3 g. lecithin. The electrodecontained no aromatic component as in the electrodes described in theforegoing examples. The electrodes initially showed almost Nernstresponse when tested in a variety of test solutions containing mixturesof sodium and potassium ions. One electrode was left standing in roomatmosphere while the other electrode was exposed to diphenyletheratmosphere. After a period of 72 hours, the first electrode showed areduction in output to almost one fourth the electrode response, whilethe second electrode which was exposed to the aromatic componentproduced almost Nernst response when tested in the test solutions. Whilethe tests on such electrodes were conducted over only a short period oftime, the advantage of subjecting the ion sensitive barrier to thevapors of an aromatic component is significiantly demonstrated by thetests.

EXAMPLE 6 Three ammonium ion measuring electrodes as described hereinwere constructed each employing an ion sensitive barrier containing 5mg. nonactin, 0.05 g. Nujol, 0.05 g. bromodiphenylether and 0.3 g.lecithin. One electrode was soaked in an aqueous solution while the twoother electrodes were exposed to atmospheres of bromodiphenylether anddiphenylether, respectively, for a period of approximately 23 days. Theelectrodes were then tested in a variety of test solutions containingmixtures of sodium and ammonium ions. The output of the latter twoelectrodes was approximately four times greater than that of theelectrode which was not exposed to the vapors of the aromatic component.The latter electrodes were again permitted to stand in the atmosphere ofthe aromatic components and tested again approximately 1 month later.The output of the electrodes was essentially unchanged.

The test which we conducted on the above electrodes and other similarelectrodes indicated that the lives of the electrodes were extended mostgreatly by exposing the electrodes to an atmosphere of diphenylether,while electrodes exposed to an atmosphere of bromodiphenylether did nothave so long a life, but the lives of such electrodes were approximatelyfour times greater than that of electrodes which remained standing inroom atmosphere between tests. The vapor pressure of diphenylether atroom temperature is about 0.1 rrim Hg. Therefore, for electrodes of thetype we tested the aromatic component employed in the container 38 ofthe present invention should have a vapor pressure close to such value.We have exposed a potassium ion measuring electrode of the typedescribed in Example 3 above to an atmosphere of ortho-xylene and foundthat the ion sensitive barrier of the electrode became quite soft, ifnot liquid, thereby greatly shortening the life of the electrode. Thus,aromatic components having vapor pressures on the order of that ofortho-xylene, approximately mm Hg, are not practical for at least someof the electrodes of the type described herein.

While several embodiments of the invention have been disclosed hereinfor purposes of illustration, it will be understood that variouschanges, alterations and modifications may be made thereto withoutdeparting from the spirit and scope of the invention as defined by theappended claims.

What is claimed is:

1. In combination, an electrode for measuring the ion activity of asolution having an ion sensitive barrier at one end thereof, saidbarrier containing a macrocyclic compound, mineral oil, an aromaticconstituent, and a sufficient amount of compound lipid to render thebarrier substantially solid, a container enclosing said one end of saidelectrode and engaging said electrode in sealing relationship, and anaromatic component in said container capable of maintaining the level ofthe voltage output of the electrode, said aromatic component having avapor pressure at room temperature substantially less than 10 mm of Hg.

2. The combination of claim 1 wherein said container comprises a bottlehaving a cap threadedly engaged thereto, said cap being formed with anopening extending therethrough, and said electrode extending throughsaid opening .with said one end positioned within said bottle.

3. The combination of claim 1 including means fixedly mounted in saidcontainer for holding said aromatic component.

4. The combination of claim 1 including a porous member fixed to thewall of said container, said aromatic component being impregnated insaid member.

5. The combination of claim 4 wherein said porous member is a sponge.

6. The combination of claim 1 wherein said aromatic component is aphenylether.

7. The combination of claim 6 wherein said component is selected fromthe group consisting of diphenylether and bromodiphenylether.

8. The combination of claim 6 wherein said component is diphenylether.

9. The combination of claim 1 wherein said macrocyclic compound isselected form the group consisting 12. The method of treating an ionmeasuring electrode so as to extend its useful life, said electrodehaving an ion sensitive barrier containing a macrocyclic compound,mineral oil, an aromatic constituent and a sufficient amount of compoundlipid to render the barrier substantially solid, comprising subjectingsaid barrier to the vapors but not the liquid of an aromatic componentfrom a source other than said aromatic constituent, said aromaticcomponent having a vapor pres sure at room temperature substantiallyless than 10 mm of Hg and being capable of maintaining the level of thevoltage output of the electrode.

13. A method as set forth in claim 12 wherein said 15. A method as setforth in claim 12 wherein said component is diphenylether.

16. A method as set forth in claim 12 wherein said barrier is subjectedto said vapors by mounting a container holding said component onto saidelectrode in sealing relationship therewith with said barrier disposedwithin said container.

17. In combination, an electrode for measuring the ion activity of asolution having an ion sensitive barrier at one end thereof, saidbarrier containing a macrocyclic compound, mineral oil, and a sufficientamount of compound lipid to render the barrier substantially solid, acontainer enclosing said one end of said electrode and engaging saidelectrode in sealing relationship, and an aromatic component in saidcontainer capable of maintaining the level of the voltage output of theelectrode, said aromatic component having a vapor pressure at roomtemperature substantially less than 10 mm of Hg.

18. The combination of claim 17 wherein said container comprises abottle having a cap threadedly engaged thereto, said cap being formedwith an opening extending therethrough, and said electrode extendingthrough said opening with said one end positioned within said bottle.

'19. The combination of claim 17 including means fixedly mounted in saidcontainer for holding said aromatic component.

20. The combination of claim 17 including a porous member fixed to thewall of said container, said aromatic component being impregnated insaid member.

21. The' combination of claim 20 wherein said porous member is a sponge.

22. The combination of claim 17 wherein said aromatic component is aphenylether.

23. The combination of claim 22 wherein said component is selected fromthe group consisting of diphenylether and bromodiphenylether.

24. The combination of claim 22 wherein said component is diphenylether.

25. The combination of claim 17 wherein said macrocyclic compound isselected from the group consisting of the monactin series, valinomycin,enniatin B, dicyclohexyl-l8-crown 6, cyclohexyl-lS-crown-S, andgramicidin, and said lipid is a phosphatide. l

26. The combination of claim 17 wherein said lipid is lecithin.

27. The combination of claim 26 wherein said macrocyclic compound isselected from the group consisting of nonactin and valinomycin.

28. The method of treating an ion measuring electrode so as to extendits useful life, said electrode having an ion sensitive barriercontaining a macrocyclic compound, mineral oil, and a sufficient amountof compound lipid to render the barrier substantially solid, comprisingsubjecting said barrier to the vapors but not to the liquid of anaromatic component having a vapor pressure at room temperaturesubstantially less than 10 mm of Hg and being capable of maintaining thelevel of the voltage output of the electrode.

29. A method as set forth'in claim 28 wherein said component is aphenylether.

30. A method as set forth in claim 28 wherein said component is selectedfrom thegroup consisting of diphenylether and bromodiphenylether.

31. A method as set forth in claim 28 wherein said component isdiphenylether.

32. A method as set forth in claim 28 wherein said barrier is subjectedto said vapors by mounting a container holding said component onto saidelectrode in sealing relationship therewith with said barrier disposedwithin said container.

1. In combination, an electrode for measuring the ion activity of asolution having an ion sensitive barrier at one end thereof, saidbarrier containing a macrocyclic compound, mineral oil, an aromaticconstituent, and a sufficient amount of compound lipid to render thebarrier substantially solid, a container enclosing said one end of saidelectrode and engaging said electrode in sealing relationship, and anaromatic component in said container capable of maintaining the level ofthe voltage output of the electrode, said aromatic component having avapor pressure at room temperature substantially less than 10 mm of Hg.2. The combination of claim 1 wherein said container comprises a bottlehaving a cap threadedly engaged thereto, said cap being formed with anopening extending therethrough, and said electrode extending throughsaid opening with said one end positioned within said bottle.
 3. Thecombination of claim 1 including means fixedly mounted in said containerfor holding said aromatic component.
 4. The combination of claim 1including a porous member fixed to the wall of said container, saidaromatic component being impregnated in said member.
 5. The combinationof claim 4 wherein said porous member is a sponge.
 6. The combination ofclaim 1 wherein said aromatic component is a phenylether.
 7. Thecombination of claim 6 wherein said component is selected from the groupconsisting of diphenylether and bromodiphenylether.
 8. The combinationof claim 6 wherein said component is diphenylether.
 9. The combinationof claim 1 wherein said macrocyclic compound is selected form the groupconsisting of the monactin series, valinomycin, enniatin B,dicyclohexyl-18-crown 6, cyclohexyl-15-crown-5, and gramicidin, and saidlipid is a phosphatide.
 10. The combination of claim 1 wherein saidlipid is lecithin.
 11. The combination of claim 10 wherein saidmacrocyclic compound is selected from the group consisting of nonactinand valinomycin.
 12. The method of treating an ion measuring electrodeso as to extend its useful life, said electrode having an ion sensitivebarrier containing a macrocyclic compound, mineral oil, an aromaticconstituent and a sufficient amount of compound lipid to render thebarrier substantially solid, comprising subjecting said barRier to thevapors but not the liquid of an aromatic component from a source otherthan said aromatic constituent, said aromatic component having a vaporpressure at room temperature substantially less than 10 mm of Hg andbeing capable of maintaining the level of the voltage output of theelectrode.
 13. A method as set forth in claim 12 wherein said componentis a phenylether.
 14. A method as set forth in claim 12 wherein saidcomponent is selected from the group consisting of diphenylether andbromodiphenylether.
 15. A method as set forth in claim 12 wherein saidcomponent is diphenylether.
 16. A method as set forth in claim 12wherein said barrier is subjected to said vapors by mounting a containerholding said component onto said electrode in sealing relationshiptherewith with said barrier disposed within said container.
 17. Incombination, an electrode for measuring the ion activity of a solutionhaving an ion sensitive barrier at one end thereof, said barriercontaining a macrocyclic compound, mineral oil, and a sufficient amountof compound lipid to render the barrier substantially solid, a containerenclosing said one end of said electrode and engaging said electrode insealing relationship, and an aromatic component in said containercapable of maintaining the level of the voltage output of the electrode,said aromatic component having a vapor pressure at room temperaturesubstantially less than 10 mm of Hg.
 18. The combination of claim 17wherein said container comprises a bottle having a cap threadedlyengaged thereto, said cap being formed with an opening extendingtherethrough, and said electrode extending through said opening withsaid one end positioned within said bottle.
 19. The combination of claim17 including means fixedly mounted in said container for holding saidaromatic component.
 20. The combination of claim 17 including a porousmember fixed to the wall of said container, said aromatic componentbeing impregnated in said member.
 21. The combination of claim 20wherein said porous member is a sponge.
 22. The combination of claim 17wherein said aromatic component is a phenylether.
 23. The combination ofclaim 22 wherein said component is selected from the group consisting ofdiphenylether and bromodiphenylether.
 24. The combination of claim 22wherein said component is diphenylether.
 25. The combination of claim 17wherein said macrocyclic compound is selected from the group consistingof the monactin series, valinomycin, enniatin B, dicyclohexyl-18-crown6, cyclohexyl-15-crown-5, and gramicidin, and said lipid is aphosphatide.
 26. The combination of claim 17 wherein said lipid islecithin.
 27. The combination of claim 26 wherein said macrocycliccompound is selected from the group consisting of nonactin andvalinomycin.
 28. The method of treating an ion measuring electrode so asto extend its useful life, said electrode having an ion sensitivebarrier containing a macrocyclic compound, mineral oil, and a sufficientamount of compound lipid to render the barrier substantially solid,comprising subjecting said barrier to the vapors but not to the liquidof an aromatic component having a vapor pressure at room temperaturesubstantially less than 10 mm of Hg and being capable of maintaining thelevel of the voltage output of the electrode.
 29. A method as set forthin claim 28 wherein said component is a phenylether.
 30. A method as setforth in claim 28 wherein said component is selected from the groupconsisting of diphenylether and bromodiphenylether.
 31. A method as setforth in claim 28 wherein said component is diphenylether.